1. Field of the Invention
The present invention relates to a map display system suited for setting a route from an arbitrary starting point (or present point) to a goal (destination) and for easily designing the route to the goal.
2. Related Art
Navigation systems with map displays function to search the optimum route to the to thereby provide guidance to the destination along the searched route. For this function, there have been proposed a variety of systems for displaying the searched route on a map screen.
The navigation system of the prior art designs the route in accordance with the input, but its starting point is always determined by the information coming from the global positioning system (GPS), i.e., the present location.
To assist setting the destination, one navigation system allows manually scrolling of the map, by referring to lists of different genres or by calling up a point registered in advance. At the reception of the GPS signal at the vehicle, the direction and straight distance from the present location to the destination are then calculated and displayed. With reference to this display, the user selects the road and direction to be followed to the destination. In the VNS system having a searching function, on the other hand, if the destination is registered as above, an optimum route from the present location is automatically determined by a search to provide guidance to the destination by voice and picture. A navigation system of this type is disclosed in Japanese Patent Laid-Open No. 66131/1993, for example.
However, the system of the prior art cannot design a route while imagining an arbitrary starting point, i.e., a virtual starting point. In other words, the conventional system cannot design a route to the destination in advance by utilizing, as a starting point, a point apart from the present location. Thus, the route cannot be planned on the basis of an input arbitrary starting point and destination, i.e., two arbitrary points freely input.
In the prior art, moreover, an optimum route can be displayed, but the screen has to be manually scrolled along a road to be observed, when it is desired to confirm the route before the start of driving. The manual scroll sequentially moves the ahead screen in the selected direction while the button or joy stick of a controller or any of (generally) eight direction touch switches of the display is operated. However, manipulation of the controller or the like while watching the movement of the map displayed on the screen is troublesome.
In either case, the information is the straight distance, direction or recommended route from the present position, as detected from the GPS received information or the sensor information received at the vehicle, so that such systems are inconvenient for use when the route is to be planned from one arbitrary point to another arbitrary point.
Calculation of the required travel time may utilize intrinsic average speed data for various types of roads such as expressways or typical national roads with determination of the distances on the individual types of roads on the set route or route determined by search of the map data. Since, however, the aforementioned method is provided with only the average vehicle speed data intrinsic to the individual kinds of roads, the average speed may differ with the various conditions such as the number of intersections per unit distance, the number of lanes, the days of the week, the time of day, the degree of business activity and the number of curves, even for the same road such as an expressway or a trunk national road. This is a disadvantage in that the estimated travel time may significantly differ from the actual travel time.